It is the purpose of this project to continue studies of cell differentiation functions in normal mammalian lymphocytes. Particular attention will be given to the role of BrdU in the inhibition of lg secretion by normal lymphocytes. The expression of cell surface antigens (h-2; membrane lg production) and the development of killer cell function will also be assessed. Recent observations of contrasting effects of unifillar BrdU incorporation into the DNA of normal lymphocytes and of plasmacytoma cell lines will be extended, with particular reference to the delineation of differentiation functions in neoplastic cells.